All things animal in Southern California and beyond

Researchers get a handle on barreleye fish (and its transparent head)

February 25, 2009 | 6:39
pm

The craziest fish we've ever seen? Perhaps. (The lanternfish is also a front-runner for that dubious honor.)

Meet Macropinna microstoma, commonly known as the "barreleye" or "spookfish." (Or as the kids might call it: "see-through head fish.") The funky fish with the transparent head was first described in 1939, but only now do researchers understand the complexities of their distinctive tubular eyes.

A recent paper by Monterey Bay Aquarium Research Institute researchers Bruce Robison and Kim Reisenbichler explains that the fish's eyes aren't fixed in place, as marine biologists had previously thought. Instead, they can rotate behind the transparent shield on the barreleye's head -- a nice adaptation for a deep-sea fish that must navigate with very little light.

The institute's website offers an explanation of how the research was conducted:

Robison and Reisenbichler used video from MBARI's remotely operated vehicles (ROVs) to study barreleyes in the deep waters just offshore of Central California. At depths of 600 to 800 meters (2,000 to 2,600 feet) below the surface, the ROV cameras typically showed these fish hanging motionless in the water, their eyes glowing a vivid green in the ROV's bright lights. The ROV video also revealed a previously undescribed feature of these fish--its eyes are surrounded by a transparent, fluid-filled shield that covers the top of the fish's head.

Beyond their most obvious feature, barreleyes also have large, flat fins that allow them to remain almost motionless in the water. The researchers speculated that the fish captures prey by staying horizontal and still with its eyes looking upward until it spots an animal like a jelly overhead. When something tasty swims above it, it rotates its eyes forward and turns to swim up and catch it.